Safety device for side dumping mechanism for a loader bucket



Aug. 11, 1970 BURCHAM ETAL 3,523,622

'SAFETY DEVICE FOR SIDE DUMPING MECHANISM FOR A LO ADER BUCKET Filed April 25, 1968 3 Sheets-Sheet l INVENTORS THOMAS L. BURCHAM STERUNG R. BOOTH,JR. WALTER B. MILLER D ONA'LD J. M RA E 7 QMJW W ATTORNEYS Aug. 11, 1970 BURCHAM ETAL 3,523,622

SAFETY DEVICE FOR SIDE DUMPING MECHANISM FOR A LOADER BUCKET Filed April 25, 1968 R J S S R Y 2 OAW E t WIHOEE M 9 AC LA 9 EROLR 0 m VU T W M M m R v. SWRD ALLEL,.1 3 HW OO/ TSWDM/ m H m Aug. 11, 1970 BURCHAM ETAL 3,523,622

' SAFETY DEVICE FOR SIDE 'DUMPING MECHANISM FOR A LOADER BUCKET Filed April 25, 1968 I5 Sheets-Sheet 5 INVENTORS THOMAS L. BURCHAM STERLING R. BOOTH JR. WALTER B. M\LLER BY DONALD J. M RAE ATTORNEYS United States Patent 01 3,523,622 Patented Aug. 11, 1970 ice 3,523,622 SAFETY DEVICE FOR SIDE DUMPING MECHANISM FOR A LOADER BUCKET Thomas L. Burcham, Peoria, Sterling R. Booth, Jr., Yates City, and Walter B. Miller, Pekin, Ill., and Donald J.

McRae, Lafayette, Calif., assignors to Caterpillar Tractor Co., Peoria, Ill., a corporation of California Filed Apr. 25, 1968, Ser. No. 724,113 Int. Cl. E07f 3/83 US. Cl. 214-768 9 Claims ABSTRACT OF THE DISCLOSURE The bucket of a loader may be pivoted to either side to dump material by disengaging one of two hydraulically operated pivot latches which normally couple opposite sides of the bucket to the loader lift arms. A hydraulic interlock system is provided between the two latches to forestall disengagement of the bucket at one side thereof if the other side is not engaged at that time.

BACKGROUND OF THE INVENTION This invention relates to loaders for handling earth or other materials and more particularly to loaders of the class having a side dumping bucket.

Two-way side dumping loaders are a highly versatile materials handling tool in that the discharge of material from the bucket can be effected by tilting the bucket to either side if desired as well as by tilting the bucket forwardly in the more conventional manner. This may provide very significant operating economies in that it is unnecessary to maneuver the loader vehicle to face the truck or other site at which the material is to be dumped. One result is that a side dumping loader can operate at a site where space is too constricted to provide for maneuvering of a forward dumping loader. Further, a loader of the type which only dumps forward in the conventional manner must almost always be driven along a repetitive curved course in maneuvering between the loading site and the dumping site. This is frequently unnecessary with a side dumping bucket in that the loader may often be maneuvered backward and forward in a more or less linear manner.

Side dumping of a loader bucket is usually arranged for by coupling each side of the bucket to the lift arms of the loader by pivot mechanisms which can be selectively unlatched. An extensible means, such as a hydraulic jack, is coupled between the central portion of the bucket and a cradle structure which spans the lift arms. Thus by unlatching one of the pivot mechanisms and extending the jack the bucket may be made to pivot towards the side which remains latched to a lift arm.

A very serious hazard can be present in this kind of loader if both pivot mechanisms are inadvertently unlatched at the same time. This hazard is particularly pronounced at the time when the operator purposely unlatches one side of the bucket in preparation for dumping. Because of soil lodging around the mechanism, distortion of the bucket or other causes, the pivot mechanism at the other side of the bucket may have failed to latch following the previous dumping cycle. The operator may not be aware of this. There is also a hazard during dumping when one side of the bucket has been deliberately unlatched and raised. Accidental shifting of the operators control can then unlatch the other side of the bucket as well.

Under these conditions, toppling of the bucket fromits cradle may be possible. As such buckets are usually bulky and heavy, very serious damage to the loader components and nearby equipment can occur in the event of such an accident. Further, there is a very serious risk of injury to personnel working on or near the loader.

While attempts have heretofore been made to reduce this hazard, the systems employed for this purpose have not been positive acting in the sense of providing a high degree of assurance that only one of the pivot mechanisms is unlatched at any given time.

SUMMARY OF THE INVENTION The present invention is a side dumping bucket mechanism which provides more positive assurance that at least one side of the bucket is latched to the supporting cradle at any given time. In particular, the two unlatchable pivot mechanisms are interconnected by a hydraulic interlock whereby unlatching of one pivot mechanism, in preparation for dumping, must force fluid to the other pivot mechanism. If the other pivot mechanism is not latched at such time, then the fluid cannot be received therein and the attempted unlatching of the first pivot mechanism cannot be accomplished. In a preferred form, the interlock system includes further means preventing accidental unlatching of a pivot mechanism at times when the other pivot mechanism has been deliberately unlatched and one side of the bucket has been raised for dumping.

Accordingly it is an object of this invention to provide a safer and more reliable side dumping loader.

The invention, together with further objects and advantages thereof, will best be understood by reference to the following description of preferred embodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a perspective view of the bucket, and adjacent structure of a ide dumping loader in accordance with the invention;

FIG. 2 is a first fragmentary section view of the disengageable pivot mechanisms which selectively couple the bucket of FIG. 1 to the supporting cradle with certain hydraulic components being shown schematically and with the mechanism in the. operating position wherein both sides of the bucket are coupled to the associated cradle;

FIG. 3 is a second section view of the pivot mechanisms corresponding to FIG. 2 but with the mechanisms in the positions assumed when one side of the bucket is decoupled from the associated cradle for dumping; and

FIG. 4 is a diagrammatic view of a second embodiment of the invention including additional components for increasing reliability and for simplifying the control manipulations required of the operator.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring initially to FIG. 1 of the drawings, the bucket 11 of a side dumping loader is carried by a pair of parallel spaced apart lift arms 12 which may be raised and lowered, suitable structure for the lift arms as well as the remainder of the loader vehicle being well known in the ,art. To control the angular position of the bucket 11 with respect to a transverse axis through the lift arms 12, tilt linkage 13 is provided. Tilt linkage 13 may be of essentially conventional construction with a forward lever 14 being coupled to the tip of each lift arm 12 by a pivot coupling 16 of the lower end of the lever. A more rearward lever 17 also has a lower end pivotably coupled to the lift arm 12. A link 18 connects the top ends of levers 14 and 17 at each lift arm and additional links 19 are pivotably connected to intermediate points on the levers 17. Links 19 extend rearwardly along the associated lift arm 12 to connect with supplementary tilt linkage in a manner well understood within the art. Such tilt linkage provides for forward dumping of the bucket 11 and for rackback movement and further tends to maintain the bucket 11 at a fixed inclination relative to the ground when the lift arms 12 are raised or lowered.

To couple the bucket 11 to lift arms 12, upper and lower tubular cradle members 21 and 22, respectively, extend transversely between the forward levers 14 and are secured thereto. Both ends of each cradle member 21 and 22 project sidewardly from the levers 14 and the projecting ends of the upper cradle member 21 are angled downward and backward whereby the corresponding ends of both cradle members 21 and 22 may connect with one of a pair of pivot latch cylinder mechanisms 23 which are aligned in an approximately horizontal direction when the lift arms 12 are elevated and the bucket 11 is racked back.

To selectively engage either or both sides of the base of the bucket 11 with the corresponding latch mechanism 23 in a pivotable manner, bracket constructions 24 are provided at each side of the base of the bucket. Each bracket construction 24 has a forward bracket member 26 and a rearward bracket member 27 which are spaced apart whereby the corresponding latch mechanism 23 may be received therebetween. The lower ends of the forward and rear bracket members 26 and 27 are angled away from each other to form ramps which facilitate engagement with the associated latch mechanism 23 as will hereinafter be discussed in more detail. Each bracket member 26 and 27 has a bore 28 for receiving a retractable pivot pin 29 at the corresponding end of the associated latch mechanism 23. Thus each side of the bucket 11 is coupled to the loader in a pivotable manner when the pins 29 at that side are engaged in the associated bracket bores 28.

To provide for side dumping of the bucket 11, a hydraulic jack 31 has a lower end coupled to the center of cradle member 21 by a pivot connection 32 and has an upper end, which is the rod end in this instance, coupled to the top of the rear wall 32 of bucket 11 at the center thereof by an additional pivot coupling 33. Accordingly, when one of the mechanisms 23 is unlatched and jack 31 is extended the bucket 11 is pivoted about the other latch mechanism to dump to one side of the loader. Extension of the jack 31 while the other latch mechanism 23 is uncoupled dumps to the opposite side of the loader.

To provide for the above described mode of operation, the operator of the loader must be provided with controls for disengaging a selected One of the latch mechanisms 23, prior to operating jack 31, to determine the particular side to which the bucket 11 is to be dumped. Further it will be apparent that severe damage and possible injury to personnel could result if both of the mechanisms 23 I were unlatched. Referring now to FIG. 2, the internal construction of the latch mechanisms 23 is shown together with a hydraulic interlock system which prevents unlatching of one pivot mechanism, in preparation for dumping, if the other pivot mechanism failed to latch following the preceding dumping cycle.

In FIG. 2 the right hand latch mechanism is designated by numeral 23 and the left hand latch mechanism is indicated by numeral 23". Each such mechanism may be comprised of a hollow cylinder 34 closed at each end by end caps 36 and having a pair of slidable pistons 37 with one piston being near each end of the cylinder. Pistons 37 are preferably situated within end sections 38' which are of slightly greater diameter than the central portion of the bore 38 through the cylinder so that inward motion of the pistons is stopped after disengagement from the associated bucket bracket members 26 and 27. A compression spring 39 is disposed coaxially within the chamber defined by the central bore 38 of each cylinder and bears against both pistons 37 to urge both pistons outwardly toward the adjacent end cap 36. Each such piston 37 carries one of the previously described pivot pins 29 which extend through openings 41 in the end caps 36, the pins being aligned with the axis of the cylinder and pistons. When pins 29 are extended in the axial direction by the action of spring 39, each pin enters the opening 28 in the associated one of the bracket members 26 and 27 of the bucket.

To facilitate the pivoting of the bucket when it is side dumped the bracket constructions 24 engage roller sleeves 40 which are rotatably mounted on the ends of the latch mechanisms 23.

Considering now the controls for disengaging a selected one of the latch mechanisms 23, a first conduit 42 or hydraulic fluid connects with both ends of the cylinder 34 of the right latch mechanism 23 through the end caps 36 thereon, whereby the application of fluid under pressure through conduit 42 retracts both pins 29 from the associated brackets 26 and 27 against the force of spring 39. A second branched conduit 43 connects with opposite ends of the cylinder 34 of the left latch mechanism 23" for similar purposes. A fluid under pressure, such as oil, is provided from a suitable source 44 which is normally already present on a loader in order to operate various other hydraulic mechanisms. The operator controls the admission of fluid from source 44 to either conduit 42 or 43 by manually shifting a dump selector spool valve 46.

Valve 46 has a normal position at which both conduits 42 and 43 are communicated with a drain 47. At this valve setting both of the latch mechanisms 23 engage the associated brackets 26 and 27 in that the pivot pins 29 of both mechanisms are extended by the action of the springs 39. Thus at this setting of the valve the bucket is coupled to the supporting structure at both sides and normal digging and forward dumping operations can be carried out in the conventional manner.

Selector valve 46 has a second setting at which fluid source 44 is communicated with conduit 42 while conduit 43 remains coupled to the drain 47. At this second setting of the valve 46, the pressurized fluid acts upon the pistons 37 within the right latch mechanism 23 to compress the spring 39 and to withdraw the pivot pins 29 from the bucket brackets 26 and 27. This releases the right side of the bucket whereby the bucket may be dumped to the left in the manner hereinbefore described.

Selector valve 46 has a third position at which fluid from source 44 is supplied to conduit 43, while conduit 42 is communicated with drain 47, to disengage the left latch mechanism 23" and thereby provide for dumping to the right in an essentially similar manner.

The use of a single selector valve 46 arranged as described above provides for a measure of safety in that only one of the mechanisms 23 can be purposely unlatched in preparation for dumping. Nevertheless, in the absence of further provisions, simultaneous uncoupling of both sides of the bucket can occur at this time.

A particularly serious problem is that earth, rocks or the like may lodge around the bucket brackets 27 and 28 or the pivot mechanisms 23. This may prevent the pivot pins 29 from coming into exact alignment with the bracket bores 28 when the bucket is lowered. Under this condition, the pivot mechanism 23 might fail to latch and the operator might be unaware of the situation. If he later unlatches the other side of the bucket in preparation for dumping, loss of the bucket can occur. The same undesirable sequence of events might also result from a bending or distortion of the bucket which prevents bores 28 from coming into alignment with pins 29.

The effects are forestalled in the present invention by connecting the central bores 38 of the two pivot mechanisms through a conduit 48 and by providing a volume of liquid such as oil within the chambers defined by bores 38 and within the connecting conduit 48. The effect of this fluid interlock is that when the pins 29 of one of the pivot mechanisms 23 are retracted as hereinbefore described to unlatch that side of the bucket in preparation for dumping, fluid is forced through the connecting conduit 48 into the central bore 38 of the other pivot mechanism 23. In order to receive the fluid, the pistons 37 and pins 29 of the other pivot mechanism must be extended, i.e. the other pivot mechanism must be latched to the bucket. If the other pivot mechanism is not latched then the attempted unlatching of the first pivot mechanism cannot be accomplished as the liquid between pistons 37 thereof cannot be received in the other pivot mechanism.

This action is illustrated in FIG. 3 wherein valve 46 is shown at the setting which supplies high pressure fluid to conduit 43 thereby retracting the pins 29 of left hand pivot mechanism 23" from the associated bucket brackets 26 and 27 in the manner previously described. The quantity of oil or other hydraulic fluid trapped within the center bores 38 of both pivot mechanisms 23' and 23" and the connecting interlock conduit 48 is selected to insure that at the above described position of one pivot mechanism 23 the pins 29 of the other pivot mechanism 23" must be engaged in the bores 28 at the other side of the bucket.

A relatively small volume of compressible gas is ineluded with the liquid within interlock conduit 48. Pro vided that the amount of such gas is suitably limited, it will not interfere with the interlocking action as described above. Generally the gas volume in an uncompressed state should not exceed the displacement of two of the pistons 37. The gas has the desirable result of reducing the cavitation effects which could occur within a cylinder 34 as the pistons 37 thereof are moved outward by the associated spring 39. The low pressure accompanying such cavitation would tend to promote leakage of oil around the pistons 37 at such times and any oil added to the interlock system by such leakage would restrict the degree to which the pins 29 can be retracted.

The apparatus of FIGS. 2 and 3 provides positive assurance against inadvertent disengagement of both sides of the bucket at a time when both sides of the bucket are down at their associated pivot mechanisms 23. While a competent operator would not deliberately manipulate selector valve 46 to release one side of the bucket while the other side was already raised clear of its pivot mechanism 23, it is preferable to provide positive assurance against an occurrence of this kind. FIG. 4 illustrates a modification of the invention having supplementary components which forestall simultaneous disengagement of both sides of the bucket at any time. The embodiment of FIG. 4 has further advantageous provisions for simplifying the control manipulation required of the operator, for compensating for possible leakage of fluid past the pistons 37 in the pivot mechanisms 23, and for replenishing the trapped fluid in the interlock system at such times as it becomes necessary.

In the embodiment of FIG. 4, the mechanical structure of the pivot mechanisms 23' and 23", dump jack 31, hydraulic interlock conduit 48 and the operators dump selector valve 46 may be similar to that hereinbefore described. However, the high pressure fluid supplied through selector valve 46 to selectively unlatch one of the pivot mechanisms 23 is derived from a source 44' through a second manually operated spool valve 49 with which the operator activates the dump jack 31 to initiate the actual dumping movement. Control valve 49 has three positions including one at which fluid under pressure from source 44' is supplied to the head end of jack 31 through a conduit 51, sequencing valve 52 and a conduit 53 from the sequencing valve to the head end of the jack, the rod end of the jack being communicated with reservoir 47' at this position of the control valve.

The control valve 49 has a second position, for returning the bucket from its dumped position, at which the high pressure fluid from source 44 is supplied to the rod end of jack 31 and the head end thereof is vented to drain 47 through the conduit 53, sequence valve 52 and conduit 51. Both ends of the damp jack 31 are blocked, thereby immobilizing the jack and bucket, when the operators control valve 49 is at the third position thereof.

Conduit 51 also connects with the dump selector valve 46 to supply high pressure fluid thereto at the first position of control valve 49. Thus, the pivot mechanisms 23 are actuated as hereinbefore described to determine the direction of bucket dumping in accordance with the setting of the selector valve 46 when the control valve 49 is shifted to the first position thereof to initiate extension of the dump jack 31. To assure that the pivot mechanisms 23 operate prior to actual movement of thedump jack 31, the sequence valve 52 includes a relief valve 54 which initially blocks fluid from the head end of the dump jack 31. Thus the initial eifect of high pressure fluid in conduit 51 is to unlatch one of the pivot mechanisms 23' or 23" according to the setting of selector valve 46. Once the pistons 37 within the pivot mechanisms have completed their travel, the pressure in conduit 51 rises opening the relief valve 54 to apply fluid to the head end of dump jack 31 to begin the dumping movement of the bucket. To provide for a return flow of fluid from the head end of jack 31 during the retraction stroke thereof, a check valve 56 bypasses the relief valve 54 within sequence valve 52.

To provide for full extension of both sets of pivot pins 29 and to reduce any tendency for leakage past the pistons 37, the first embodiment of the invention included a small amount of compressible air in the interlock passages. In the present embodiment of FIG. 4, similar results are provided for by coupling an accumulator 57 to the interlock conduit 48. Accumulator 57 has a stop 58 which restricts the volume of liquid which can be withdrawn from the interlock conduit to an amount which is insulficient to interfere with the desired interlocking action but which is adequate to provide for full extension of both sets of pins 29 into the associated bucket bores 28. This is generally a volume which does not exceed the displacement of one pair of pistons 37.

To provide for introduction of hydraulic fluid into the interlock system, a valve 59 may be connected between the interlock conduit 48 and one of the conduits 42 or 43 to which the pivot mechanisms are actuated, the valve being connected to conduit 43 in this example. Bleed valves 60 are provided at the bore 38 of each pivot mechanism and at accumulator 57. With all bleed valves 60 opened and valve 59 open as well, the proper amount of liquid can be put into the interlock system by holding one set of pivot pins 29 contracted and shifting control valve 49 and selector valve 46 to supply fluid through conduit 43. Valves 59 and 60 are of course closed after the interlock has been filled.

In the embodiment of the invention described with reference to FIGS. 1 to 3, angled ramps are provided at the lower ends of the brackets 26 and 27 which engage with the pivot mechanisms 23 in order to force retraction of the pivot pins 29 as the bucket is returned from its dumping position. Referring now again to FIG. 4 an alternate means for accomplishing the same purpose is shown which avoids the need for angling the lower ends of the brackets 26 and 27.

In particular, a flow restriction 61 is provided in conduit 51 between the control valve 49 and the sequence valve 52 and selector valve 46, the flow restriction being bypassed by a check valve 62 which provides for relatively unrestricted flow ina direction towards sequence valve 52 and selector valve 46 whereby extension of jack 31 for dumping purposes is not impeded. During return of the bucket to the loading position by contraction of jack 31, the effect of the flow restriction 61 is to generate a strong back pressure in conduit 42 or 43 according to the setting of valve 46. This back pressure maintains the pivot pins 29 of the appropriate pivot mechanism 23 or 23" in a retracted condition until the pins have moved between the brackets 26 and 27 and have arrived in alignment with the associated bores 28.

The system of FIG. 4 operates in the manner hereinbefore described to prevent uncoupling of one side of the bucket at a time when the other side of the bucket failed to engage following the preceding dumping operation. However the embodiment of FIG. 4 is provided with an additional safety means which prevents uncoupling of one side of the bucket, by accidental manipulation of the selector valve 46, at a time when the other side has been lifted clear of its pivot mechanism 23 as occurs in the course of dumping. In particular, a blocker valve 63 is disposed in the interlock conduit 48. Blocker valve 63 is arranged to be open when both sides of the bucket 11 are down at the associated pivot mechanisms 23 and thus at such times the blocker valve does not interfere with the interlocking action as hereinbefore described. The blocker valve 63 is further arranged to close whenever either side of the bucket is lifted from its pivot mechanism. With the blocker valve 63 closed, flow through the interlock conduit 48 is stopped and the particular pivot mechanism 23 which is engaging the bucket at that time continues to do so because of the volume of liquid which is now trapped between its extended pistons 37. Such pivot mechanism 23 can be unlatched only after the bucket has returned to its lowered position thereby again opening the blocker valve 63.

Various arrangements are possible for controlling the blocker valve 63 in the above described manner. The valve 63 may, for example, be a normally closed type and have an actuator positioned to be contacted by the base of the bucket as it arrives at its lowered position. In the present example as shown in FIG. 4, the blocker valve 63 is a normally open type and has a hydraulic actuator 63 responsive to fluid pressure in the conduit 53 which connects with the head end of the dumping jack 31. Thus actuator 63' closes the normally open blocker valve 63 at such times as there is significant fluid pressure in the head end of the dumping jack 31. This provides the desired control of blocker valve 63 in that some degree of pressure is present at the head end of the dumping jack 31 at all times except when the bucket is down with both sides thereof at the associated pivot mechanism 23.

While the invention has been described with reference to certain exemplary embodiments, it will be apparent that many modifications are possible and it is not intended to limit the invention except as defined in the following claims.

What is claimed is:

1. In a side dumping loader, the combination comprising:

a bucket carried by said loader;

a pair of latches for selectively coupling separated portions of said bucket to said loader in a pivotable manner, each of said latches having a liquid containing chamber therein and having a piston which moves to reduce the volume of said chamber as said latch is disengaging,

a liquid containing interlock conduit connecting said liquid containing fluid chambers of said pair of latches, said conduit and said chambers together forming a closed hydraulic system, said liquid in said closed hydraulic system serving to positively prevent disengagement of one of said latches in response to failure of the other of said latches to engage, the amount of liquid in said closed hydraulic system being such that both of said latches cannot be simultaneously disengaged, means enabling both of said latches to be simultaneously engaged, and

means for pivoting said bucket about a selected one of said latches to effect a dumping movement thereof.

2. The combination defined in claim 1 wherein said fluid chambers of said latches and said interlock conduit contain a liquid together with a compressible gas, the volume of compressible gas being suflicient to reduce cavitation in said chambers when both of said latches are in the engaged position and being insuflicient to provide for simultaneous disengaging of both latches.

3. The combination defined in claim 1 further comprising an accumulator coupled to said interlock conduit, said accumulator having a fluid capacity limited to substantially the amount of fluid which is expelled from one of said latches into said interlock conduit by said disengaging movement of said piston.

4. The combination defined in claim 1 wherein each of said latches is actuated by fluid supplied thereto through additional conduits extending to an operators selector valve, and further comprising a bleed valve at each of said latches and an additional valve coupled between said interlock conduit and at least one of said additional conduits whereby said chambers may be filled with the fluid through said selector valve.

5. The combination defined in claim 1 further comprising a blocker valve operative upon said interlock conduit and having an open position providing for flow through said conduit and a closed position blocking flow therethrough, and means maintaining said blocker valve closed when said bucket has been pivoted away from either one of said latches.

'6. The combination defined in claim 1 wherein said means for pivoting said bucket is a fluid pressure operated jack connected between said bucket and said loader and wherein said latches are disengageable by the application of fluid thereto at a first pressure level, further comprising an operators dump control valve coupled to said jack for selectively applying pressurized fluid thereto and coupled to said latches for applying said fluid to a selected one thereof, and a sequence valve coupled between said jack and said operators dump control valve, said sequence valve being of the class which opens when the fluid pressure from said dump control valve reaches a predetermined pressure which is greater than said first pressure.

7. The combination defined in claim 6 further comprising a flow restriction in the flow passage from said sequence valve and said latches to said dump control valve, and a check valve bypassing said flow restriction to provide for relatively unrestricted flow from said dump control valve towards said sequence valve and said latches.

8. The combination defined in claim 6 further comprising a normally open blocker valve in said interlock conduit, said valve having a fluid operated actuator responsive to fluid pressure in said jack whereby said interlock conduit is blocked while said jack is operating.

9. In a side dumping loader of the class having a bucket carried on a pair of lift arms and having means for pivoting said bucket sidewardly relative to said lift arms, the combination comprising a pair of latches carried on said lift arms and situated at opposite sides of the base of said bucket for selectively engaging therewith, each of said latches having a hydraulic cylinder with a pair of spaced apart pistons therein, each of said pistons carrying a pin which can be extended from an end of said cylinder by motion of the associated piston to engage said bucket and which can be retracted by opposite motion of said associated piston to disengage from said bucket,

means for admitting high pressure fluid to the ends of a selected one of said latch cylinders to retract said pins thereof and release one side of said bucket from said lift arms, and

a fluid containing interlock conduit connecting said hydraulic cylinders between said pistons of said pair of latches, said conduit and the cylinder portions between said pistons together forming a closed hydraulic system, said fluid in said closed hydraulic system serving to positively prevent disengagement of one of said latches in response to failure of the other ofsaid latches to engage, the amount of fluid in said closed hydraulic system being such that both of said latches cannot be simultaneously disengaged, and means enabling both of said latches to be simultaneously engaged.

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